Wear occurs on surfaces which are in sliding contact with one another. High loads can accelerate the rate at which wear occurs. Traditional bearings have metal-on-metal sliding surfaces. Such metal-on-metal bearings require lubrication to reduce friction between the sliding surfaces. If the surface is not properly lubricated the bearing and any associated machinery can be irreparably damaged.
It is known to treat sliding surfaces with a low friction application to reduce friction between the sliding surfaces. A sliding surface treated with a low friction application may be referred to as a self-lubricating surface. Known low friction applications include, but are not limited to, rubber, ceramic, fabric, and resins with lubricant fillers such as polytetrafluoroethylene (PTFE), graphite, and a molybdenum sulfide.
It is further known to use such low friction treatment with spherical bearings. Spherical plain bearings typically have a steel alloy or ceramic ball positioned in a steel alloy race. The race defines an inner surface contoured to receive the spherical ball therein. A lubricant, such as grease, is typically provided between the spherical ball and race to reduce friction during operation. To reduce the need for lubrication, or in lieu of using a lubricant, it is known to apply a low friction treatment to one or more of the bearing surface and or the contoured inner surface of the race.
Despite recent improvements in this technology, many self-lubricating bearings experience ingress of contaminants that degrade the bearing and the self-lubricating coating compositions. Common contaminants may include sand, mud, and particulate contamination. The contaminants enter the bearing between the race and the ball and degrade the sliding surface between the race and the ball.
This problem is especially prevalent for heavy load vehicles used in harsh environments, such as military equipment, construction vehicles, hauling vehicles, mining equipment, and fire trucks. Contamination of the coating composition leads to a rapid increase in the wear rate of the bearing and, in turn, decreases the life of the bearing. Accordingly, a self-lubricating bearing capable of inhibiting contamination of the self coating composition, while maintaining the integrity and usefulness of the bearing is needed.